1. Field of the Invention
The present invention relates to a magnetoresistance (or magneto-resistance) effect element particularly provided with Ballistic Magneto Resistance (BMR) effect and also relates to a magnetic head provided with such magnetoresistance effect element.
2. Relevant Art
Generally, a giant magnetoresistance effect (GMR effect) is a phenomenon indicating rate of change in magnetoresistance (called herein MR ratio) which is developed or reviled in a case that electric current passes in a plane of a lamination structure of ferromagnetic layer/non-magnetic layer/ferromagnetic layer. Moreover, the magnetoresistance effect element of such GMR has been further actively studied for the development of more large MR ratio, and up to now, ferromagnetic tunnel junction and a CPP (Current Perpendicular to Plane)-type MR element, in which the current passes perpendicularly with respect to the lamination structure, have been developed, and hence, has high degree of expectation for reproducing (regenerative) element for magnetic sensor, magnetic recording element and the like.
In the field of the magnetic recording technology, according to improvement of recording density, it has been a progress to make compact recording bits, and as its result, it becomes difficult to obtain a sufficient signal strength. Thus, taking such matters into consideration, it has been desired for engineers in this field to search a material having high sensitive magnetoresistance effect and develop or revile an element indicating a large MR ratio.
Recently, there have been reported, as material indicating MR ratio of more than 100%, “magnetic micro contact” which is formed by butting two needle-like nickel (Ni) as shown, for example, in a document of “Physical Review Letters, vol. 82, p 2923 (1999), by N. Garcia, M. Munoz, and Y.-W. Zhao” (Document 1). This magnetic micro contact is manufactured by butting two ferromagnetic materials arranged in form of needle or in form of triangle. More recently, there has been developed a magnetic micro contact in which two fine Ni wires are arranged in T-shape and micro column is grown at a contact portion of these wires by electro-deposition method (for example, refer to a document of “Appl. Phys. Lett. Vol. 80, p 1785 (2002), by N. Garcia, G. G. Qian, and I. G. Sveliev” (Document 2).
It is considered that an extremely high MR ratio developing such element is based on spin transport of a magnetic area existing in the magnetic nano contact formed between two ferromagnetic layers having magnetized directions in anti-parallel to each other. It is considered that, in the magnetoresistance effect element utilizing the magnetic nano contact having such characteristics, since electrons pass without receiving any scattering or diffusion (i.e., pass ballistically), such magnetoresistance effect element is called BMR element (Ballistic Magneto Resistance element).
In addition, more recently, there has also been reported a magnetoresistance effect element having such magnetic nano contact. For example, in Japanese Patent Laid-open (KOKAI) Publication No. 2003-204095 (Document 3), there is reported a magnetoresistance effect element composed of first ferromagnetic layer/insulating layer/second ferromagnetic layer, in which the first ferromagnetic layer is connected to the second ferromagnetic layer at a predetermined portion of the insulating layer, the magnetoresistance effect element being provided with a hole having the maximum diameter of less than 20 nm. Furthermore, in Japanese Patent Application National Publication (Laid-open) No. HEI 11-510911 (Document 4), there is reported a magneto-resistance effect element composed of two magnetic layers connected to each other through a narrow segment having a width of about 100 nm.
However, in consideration of application of a BMR element to a magnetic head, a dimension of a free layer sensitive to magnetic field leaking from a surface of a medium is made small such as, for example, to several tens nm. In a case of recording density of 1 Tbits/in2, a read head of 40 to 50 nm width is required, and in a case of a BMR element capable of realizing an extremely high MR ratio, a structure of a magnetic domain of the magnetic nano contact (called hereinlater “nano-contact portion”) is a “key” of the DMR effect As the read head miniaturization progresses, strong demagnetizing magnetic field is generated from the end face of the fine free layer, which results in a degradation of its thermal instability, being inconvenient and disadvantageous. Therefore, in the BMR element, it is an extremely important object to ensure the magnetic domain control and magnetic stability thereof.